1. Field of the Invention
The present invention relates to a switch circuit having plural points of contact and providing a signal to discriminate the operation state of each point of contact and, more particularly, to a switch circuit that is suitable to detect the size of the transfer paper in the paper feed cassette attached to the main body of the copying apparatus.
2. Description of the Prior Art
FIG. 1 is an electric circuit diagram of a conventional switch circuit for discriminating the size of the transfer paper in a copying apparatus. In FIG. 1, S11, S21, S31, S41, S51 and S61 are the switches attached to the main body side of the apparatus, S11 through S51 are the switches to detect the size of the transfer paper and, S61 is a switch to detect the existence of the transfer paper. It is so constituted that one of the switches S11-S51 is closed by the protrusion provided on each paper feeding cassette corresponding to the size of the transfer paper when the paper feeding cassette is inserted, and the switch S61 is closed when transfer paper is present. CO is a connector, IP is an input terminal and CC is a control circuit. Switches S11-S61 are connected to the input terminal IP through the connector CO and the signal therefrom is inputted to the control circuit CC. Symbols l0, l1, l2, l3, l4, l5 and l6 are lead wires that connect one side of the connector CO to switches S11-S61. Symbols l0', l1', l2', l3', l4', l5' and l6' are lead wires that connect the other side of the connector CO to the input terminal IP. In each lead wire, the one having the same suffix in its symbol is electrically connected through the connector CO to the other lead. A closed circuit consisting of lead wires l0', l0, l1' and l1 and switch S11 is formed when the switch S11 is closed; a closed circuit consisting of lead wires l0', l0, l2' and l2 and switch S21 is formed when the switch S21 is closed; a closed circuit consisting of lead wires l0', l0, l3' and l3 and switch S31 is formed when the switch S31 is closed; a closed circuit consisting of lead wires l0', l0, l4 and l4' and switch S41 is formed when the switch S41 is closed; a closed circuit consisting of lead wires l0', l0, l5 and l5' and switch S51 is formed when the switch S51 is closed; and a closed circuit consisting of lead wires l0', l0, l6 and l6' and switch S61 is formed when the switch S61 is closed. Symbols L1, L2, L3, L4, L5 and L6 are luminous elements that indicate the size of the transfer paper and are arranged on the indicator part of the main body of the apparatus. These luminous elements L1-L6 are connected to the control circuit CC through the output terminal OP. The luminous element L1 is operated by the control circuit CC when the switch S11 is closed and it indicates the size of the transfer paper contained in the paper feeding cassette that has closed the switch S11. In the same manner, the luminous element L2 is operated by the control circuit CC when the switch S21 is closed, the luminous element L3 is operated by the control circuit CC when the switch S31 is closed, the luminous element L4 is operated by the control circuit CC when the switch S41 is closed, the luminous element L5 is operated by the control circuit CC when the switch S51 is closed and the luminous element L6 is operated by the control circuit CC when the switch S61 is closed. Thus the size of the transfer paper in the paper feeding cassette or the existence of the transfer paper therein is indicated.
In the conventional switch circuit, there has been a problem that lead wires in the quantity corresponding to the number of switches, the connector CO having pins in the quantity corresponding to the number of switches and the input terminal IP and the output terminal OP both having terminals in the quantity corresponding to the number of switches are needed and therefore, the wiring is complicated and the reliability is lowered accordingly. Also, there has been a problem that actual installation of the connector having many pins and the input/output terminals having many terminals have caused the cost to be high.